1. Field of the Invention
The present invention, in general, relates to electrical connectors and, more particularly, to electrical connectors that are used to supply electrical power to an aircraft and which are field-replaceable.
In order to energize the electrical systems of an aircraft without running a generator on-board the aircraft, an electrical cable is used to supply 400 Hz electrical power to the aircraft. Typically, the electrical power that is supplied is three phase and is at approximately 200 volts (AC).
The mating interface on the plug on the end of the cable which mates to the aircraft is standardized by adherence to U.S. Military Specification MIL-C7974.
Switches are sometimes installed in the connector plug and are used to actuate a device to extend or retract additional lengths of cable off of a spool or to cycle power to the aircraft through the cable at appropriate times. For example, it is not appropriate to supply electrical power the moment an electrical connection is made because this can damage the electrical contacts.
Similarly, it is not appropriate to use physical disengagement of the connector as a means of withdrawing electrical power from the aircraft. As is well known in the electrical arts, this will cause arcing to occur and will in turn damage the electrical contacts.
A plurality of switches (typically up to four switches) and a plurality of lights (to indicate switch function, power status, or other) may optionally be included in these and various types of connectors.
To cycle power, xe2x80x9conxe2x80x9d and xe2x80x9coffxe2x80x9d switches are used to energize and de-energize a relay at the source of electrical power on the ground. The xe2x80x9conxe2x80x9d switch can then be depressed to energize power to the aircraft only after the connector is properly mated to the aircraft and, conversely, the xe2x80x9coffxe2x80x9d switch can be depressed to de-energize electrical power before any attempt is made to remove the connector from the aircraft.
The on and off switches are optional in these types of connectors. The use of a recessed contact is also generally used in these types of connectors to prevent the application of electrical power to the aircraft until a sufficiency of mating amongst the contacts that actually supply electrical power to the aircraft has first been accomplished.
However, the defect to this purely mechanical approach to regulating the application of electrical power to the aircraft is that if a person abruptly jerks the connector apart from the aircraft, there remains the potential for damage to occur to the contacts as a result of the subsequent arcing that is likely to occur.
The other common types of switches are typically labeled xe2x80x9cinxe2x80x9d and xe2x80x9coutxe2x80x9d. When the xe2x80x9cinxe2x80x9d switch is depressed, the spool will wind in such a direction so as to retract the cable and when the xe2x80x9coutxe2x80x9d switch is depressed, the spool will unwind and spool out additional cable to reach the aircraft. A cable hoist is often used in place of a spool, with the same effects.
Often, the plug that is disposed at the end of the electrical cable is molded (i.e., it is made of a type of rubber) and it is permanently attached to the cable by the manufacturer. Therefore, it cannot be replaced in the field. A molded plug that is durable and can be replaced in the field is desirable.
It is far more likely that defects will arise in or proximate the connector than elsewhere in the cable itself. Obviously, if a defect should arise in the connector, it is advantageous to be able to replace the connector instead of the entire cable. Such a connector is known in the arts as one that is xe2x80x9cfield attachablexe2x80x9d or xe2x80x9cfield replaceablexe2x80x9d.
It is known according to the present state of the art to utilize a replaceable contact section, sometimes called a xe2x80x9cnosexe2x80x9d, as is disclosed in U.S. Pat. No. 4,758,175 and which is incorporated by reference herein. This permits the end user to replace this portion of the connector when needed due to abrasion or other types of damage that may occur.
The preceeding type of nose is typically attached to a another component, a nose insert that is surrounded by a split two-part plastic body housing which is filled with epoxy that is allowed to flow into the housing through the switch hole(s). There are problems associated with this approach.
The first is that the two-part plastic body housing does not provide an adequate seal to prevent epoxy from leaking out. While not posing a problem in performance, this is undesirable from an aesthetic point of view.
Also, the plastic that the body housing is made of tends itself to loosen and wear over the course of time. As such, it may develop slack. A strain relief is typically added as well and it serves to limit the bend radius.
A maintenance schedule may be established to periodically tighten any clamps or screws and to take up slack that may develop (due to a general loosening or wear).
However, there is no way to really know if any established maintenance schedule is correct. If maintenance is done too often, there is an excess of labor. If it is not done often enough, the result is ineffective strain relief and premature wear and failure. Without adequate strain relief when removing the cable from the aircraft, the person may be pulling on the individual conductors, rather than on the jacket and connector. This can cause premature wear and conductor failure to occur.
Also, due to size constraints, the plastic body housing is thin and the two halves may move in shear with respect to one-another. The two halves may also tend to separate and, as mentioned hereinabove, epoxy may tend to leak out before it has fully set.
The epoxy potting is necessary in order to meet the required specifications and also to provide the durability that is needed. These connectors may, for example, be dropped, dragged, or run over by machinery that is being operated nearby (e.g., ramp tractors). Therefore, the connectors must be resistant to crushing and also to other types of severe loading that they may experience.
Also, when these connectors are inserted (or withdrawn), a great deal of force is typically required, a force that is normally measured in the xe2x80x9ctensxe2x80x9d of pounds. The force to insert the connector into the aircraft can even approach or exceed one-hundred pounds of force. Field personnel expect this and it is not an issue other than to note that these connectors are subject to substantial forces that occur during their insertion and removal.
The aforementioned problems and requirements for connecting power to an aircraft tend to be extreme and therefore are poised to maximally benefit from the instant disclosure. However, the invention is applicable, as desired, for use in various applications other than those involving aircraft. In general, wherever a durable field replaceable type of a connector is required, the benefits and uses as disclosed herein, apply.
Accordingly there exists today a need for a field attachable electrical connector and self-tightening method of strain relief that helps to reduce the aforementioned problems.
Clearly, such an apparatus would provide a useful and desirable device and method.
2. Description of Prior Art
Electrical connectors are, in general, known. While the structural arrangements of the known types of devices, at first appearance, may have similarities with the present invention, they differ in material respects. These differences, which will be described in more detail hereinafter, are essential for the effective use of the invention and which admit of the advantages that are not available with the prior devices.
It is an object of the present invention to provide a field attachable electrical connector that can be replaced in the field.
It is also an important object of the invention to provide a field attachable electrical connector that is durable.
Another object of the invention is to provide a field attachable electrical connector that includes means for resisting motion between two halves of a body housing in shear.
Still another object of the invention is to provide a field attachable electrical connector that includes means for resisting separation from occurring between two halves of a body housing.
Still yet another object of the invention is to provide a field attachable electrical connector that provides a method for adjusting the amount of strain relief automatically during normal use.
Yet another important object of the invention is to provide a field attachable electrical connector and self-tightening method of strain relief that uses the force that is required to insert the connector into the aircraft to automatically take up (i.e., compensate) for any slack that may have occurred over time and use.
Still yet another important object of the invention is to provide a field attachable electrical connector and self-tightening method of strain relief that is adapted to satisfy the requirements of U.S. Military Specification xe2x80x9cMIL-C-7974xe2x80x9d.
Briefly, a field attachable electrical connector and self-tightening method of strain relief that is constructed in accordance with the principles of the present invention has a split plastic body housing consisting of two halves that includes a pair of retaining grooves on each of the two halves, the retaining grooves being adapted to fill with epoxy and to retain the two halves adjacent to each other. A plurality of pins on one of the halves fits into a plurality of holes on the remaining one of the halves when the two halves are adjoined, thereby reducing shear. The body housing is adapted to contain a plastic nose insert, an elastomeric nose, a plurality of crimp contacts, a plurality of switches and lights, and the necessary wiring. When the two halves are properly oriented adjacent to each other, a distal end of each of the two halves that is disposed opposite to that where the elastomeric nose is disposed includes a ratcheting cable retention system. The ratcheting cable retention system provides automatic adjustment of a strain relief that passes over the cable. The strain relief is pressed over a plurality of fingers that are attached to the two halves of the body housing. The strain relief thereby serves to retain the distal ends adjacent to each other. Furthermore, the strain relief cooperates with a tapered ratcheting system on the fingers so that when the connector is pushed into the aircraft the strain relief is grasped and is used to push the connector into mating with the aircraft. Any slack that may have developed over time between the fingers and the cable that is disposed under the fingers is automatically removed by the strain relief being urged closer to the two body halves, thereby tightening the fingers against the cable.